Re: [PATCH RESEND] device_cgroup: Fix RCU list debugging warning
From: Stephen Rothwell <hidden>
Date: 2020-06-06 20:23:49
Also in:
linux-kernel-mentees, lkml
Hi all, On Mon, 6 Apr 2020 16:29:50 +0530 Amol Grover [off-list ref] wrote:
quoted hunk ↗ jump to hunk
exceptions may be traversed using list_for_each_entry_rcu() outside of an RCU read side critical section BUT under the protection of decgroup_mutex. Hence add the corresponding lockdep expression to fix the following false-positive warning: [ 2.304417] ============================= [ 2.304418] WARNING: suspicious RCU usage [ 2.304420] 5.5.4-stable #17 Tainted: G E [ 2.304422] ----------------------------- [ 2.304424] security/device_cgroup.c:355 RCU-list traversed in non-reader section!! Signed-off-by: Amol Grover <redacted> --- security/device_cgroup.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)diff --git a/security/device_cgroup.c b/security/device_cgroup.c index 7d0f8f7431ff..b7da9e0970d9 100644 --- a/security/device_cgroup.c +++ b/security/device_cgroup.c@@ -352,7 +352,8 @@ static bool match_exception_partial(struct list_head *exceptions, short type, { struct dev_exception_item *ex; - list_for_each_entry_rcu(ex, exceptions, list) { + list_for_each_entry_rcu(ex, exceptions, list, + lockdep_is_held(&devcgroup_mutex)) { if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK)) continue; if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))-- 2.24.1
I have been carrying the above patch in linux-next for some time now. I have been carrying it because it fixes problems for syzbot (see the third warning in https://lore.kernel.org/linux-next/CACT4Y+YnjK+kq0pfb5fe-q1bqe2T1jq_mvKHf--Z80Z3wkyK1Q@mail.gmail.com/ (local)). Is there some reason it has not been applied to some tree? -- Cheers, Stephen Rothwell
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